What are the key differences between reactive black and sulphur black in textile dyeing?

What are the key differences between reactive black and sulphur black in textile dyeing?
Sulphur Black 1 and reactive dyes operate on fundamentally different mechanisms. Sulphur dyes are insoluble in water and require reduction with sodium sulfide to form a soluble leuco form with thiol groups that carry only one negative charge per group. This results in lower electrostatic repulsion with negatively charged cellulose fibers compared to reactive dyes, which carry sulfonate groups with two negative charges. Consequently, sulphur black dyeing needs less Glauber's salt (sodium sulfate) than reactive dyeing. However, sulphur dyeing generates toxic gases and requires oxidation post-treatment to re-insolubilize the dye on fiber. Reactive dyeing, while requiring large salt amounts and alkaline conditions (pH ~10), offers better environmental profile but slightly lower wash fastness due to residual soluble dye. Sulphur black generally provides superior color fastness, making it preferred for heavy-duty textiles like denim and workwear.